Nicola Sturgeon will “restart the debate” on independence this week with the publication of a long-awaited report on what Scotland’s economy would look like outside the UK.

The First Minister claimed the report from the SNP’s Growth Commission, expected after 18 months of work, will jump-start a discussion over Scotland’s constitutional future based on “ambition and hope”.

Nicola Sturgeon. Picture: PA

Led by former SNP adviser Andrew Wilson, the commission is expected to make the case for an independent Scotland to have its own currency in the event of a Yes vote.

The report’s release comes as a poll found nearly two-thirds of voters in Scotland believed Brexit could lead to the break-up of the UK.

Opposition leaders accused the First Minister of reheating old arguments from the 2014 referendum campaign, but Scottish Conservative leader Ruth Davidson issued a call to action for the “London-centric” UK establishment to protect the Union.

Ms Sturgeon told ITV’s Peston on Sunday programme the report’s release was an “important moment” that would set the agenda for the debate on independence. Asked when she would reveal when a second independence referendum might take place, she said: “Once we get some clarity, which hopefully we will in the autumn of this year, about the Brexit outcome and the future relationship between the UK and the EU, then I will consider again the question of the timing of an independence referendum.

“I’m not going to say more about that in advance of that moment arising.

“Of course, over the next couple of weeks we will restart a debate about why independence for Scotland is an opportunity and what those opportunities are.

“We’ve had a Growth Commission looking at the economic opportunities of independence.

“Its report will be published in the coming days and I think that’s quite an important moment because if you think about the last couple of years in the UK, it’s been very much a debate about how we cope with the damage of Brexit.

“What I think Scotland now has the opportunity to do is to look at how we seize the opportunities that lie ahead – a debate that’s based on ambition and hope, not a debate that’s based on despair, which is how the Brexit debate very often feels.”

The Growth Commission report has been repeatedly delayed and is claimed to have cost the party £120,000 to produce.

The document is expected to make suggestions to overcome sluggish growth that has left Scotland lagging behind the rest of the UK. One source close to the commission has been quoted as saying the report would acknowledge the economy was “not firing on all cylinders”.

On the currency, the report is expected to set out a gradual transition after independence, with Scotland initially using the pound while a new central bank is set up.

However, Scottish Labour leader Richard Leonard said: “The idea that a separate Scotland would seek to use the pound without a central bank behind it is a recipe for instability and is the economics of dereliction.”

Ms Sturgeon’s comments came as polling on the eve of a major conference on constitution showed widespread support for the Union but widespread concern over its future.

The poll by the Policy Exchange think-tank, which will host today’s gathering of past and present Scottish political leaders in London, found that all four nations of the UK backed the Union, but support was lowest in Scotland at 52 per cent. This compared with 68 per cent in England, 66 per cent in Wales and 59 per cent in Northern Ireland.

More than half of Scots (59 per cent) believe Brexit makes the break-up of the UK more likely.

Ms Davidson, who will close the Policy Exchange event with a defence of the Union, yesterday warned that the UK was “still too London-centric” and called for British institutions to do more to help strengthen the UK.

She said: “As long as our future relationship with the EU is in flux, it would be foolish to assume that the current trends on Scotland remaining in the UK will hold and that the threat of separation has gone away.”